Technical Abstract:
The major genes for sunflower downy mildew resistance have been designated as Pl genes. Many Pl genes have been reported, with 10 of them having been mapped. In this study, we report the molecular mapping of the Pl gene in a downy mildew differential line HA-R4, which has been temporarily named PlHA-R4. It was mapped on the lower end of the linkage group (LG) 1 of the sunflower reference map, with 11 markers covering a genetic distance of 78.9 cM. One dominant marker ORS 1008 co-segregated with it, and another marker HT 636 was at a genetic distance of 0.3 cM proximal to this gene. Marker ORS 1008 was used to test 37 other germplasms. The data suggests that the Pl genes in HA-R4 and HA-R5 are different from other germplasms tested. The two tightly linked markers will be helpful for marker-assisted selection (MAS) in sunflower breeding, as well as molecular cloning of this gene.